1. Industrial Field of the Invention
This invention relates to a hole saw for use in cutting out holes of comparatively large diameters.
2. Prior Art
There are known hole saws of the type having a hole saw body and a shank for removably mounting the hole saw body to the tool mounting portion (main shaft portion) of a portable electric drill, with the hole saw body and shank being integrally fixed to each other. Such known hole saws are very uneconomical in the case of the saw tooth portion being worn away or damaged, because the entire hole saw including the shank must be replaced.
Also known in the art is a hole saw of the type comprising a threaded portion formed at the front end of the shank and a threaded hole formed in a base crossing the cylinder of the hole saw body, whereby the hole saw body can be removably mounted to the shank by bringing the threaded hole of the hole saw body into thread engagement with the threaded portion of the shank (as described in, for example, Japanese Utility Model Application Laid-Open Publication No. 55 - 169309).
Such a hole saw construction involves a drawback that since the means for removably mounting the hole saw body to the shank take the form of thread engagement between the two elements, an attempt to replace the hole saw body with another one after the hole saw has been operated is likely to encounter a difficulty such that, because of the rotation torque of the shank and reaction force of the hole saw body against the torque during the operation, the threaded portions of the shank and hole saw body have become so tightly engaged that it is very difficult to turn back the threaded portions. This means considerable inconvenience and danger is involved in replacing the hole saw body.
As a typical example of state-of-the-art arrangement which has solved such a problem, a hole saw of the following type is found among presently commercially available hole saws (see FIGS. 9 and 10). This hole saw 43 has a threaded portion 32 formed on a shank 31 at the front end thereof, and a threaded hole 35 formed in a base 34 crossing the axis of a hole saw body 33. A stopper 38, consisting of a disc 36 having a hole for receiving the shank 31 and a pair of pins 37 projecting from the disc 36, is fitted on the shank 31 side of the hole saw 43. The pins 37 are received in guide grooves 40 formed in a large-diameter portion 39 of the shank 31 so that the stopper 38 is supported non-rotatably relative to the shank 31 but slidably in the axial direction of the shank. Further, a nut 41 for locking the stopper 38 at its advanced position at which the stopper 38 contacts the large-diameter portion is threadably mounted on the shank 31 of the hole saw 43, and holes 42 for receiving the pins 37 of the stopper 38 are bored in the base 34 of the hole saw body 33.
Therefore, this hole saw 43 is such that, when the hole saw body 33 is brought in thread engagement with the shank 31, if the pins 37 of the stopper positionally coincide with the holes 42, the stopper 38 is advanced until the pins 37 are satisfactorily received into the holes 42, and if positional coincidence is not reached, the hole saw body 33 is screwed back until positional coincidence is reached and then the stopper 38 is advanced for insertion of the pins 37 into the holes 42. Through such process the hole saw body 33 can be non-rotatably mounted in position relative to the shank 31, and the nut 41 serves to prevent slip-off of the pins, 37.